The Alzheimer’s Society is the UK’s leading care and research charity for people with dementia, their families and carers. They produce information and advice sheets to support those affected by dementia. Prions are infectious agents that attack the central nervous system and then invade the brain, causing dementia. The best-known prion disease is Creutzfeldt-Jakob disease, or CJD. This information sheet provides an overview of the symptoms and different types of CJD.